Tire cord, especially, tire cord treated by an adhesive has been generally used as reinforcing materials for pneumatic tires. The tire cord may be made of nylon fiber, polyester fiber, or cellulose-based modified natural fiber. Among methods for improving performance of finally-obtained rubber products is to enhance the property of the tire cord used as the reinforcing material.
Generally, the nylon fiber having great elongation and strength may be used as reinforcing materials for the tires of large truck applied with a high load, and vehicle driven on a road with a rough surface, for example, an unpaved road. However, since the nylon fiber has a low modulus, the nylon fiber is unsuitable for a racing car driven with high speed, and an automobile requiring a smooth and comfortable ride.
The polyester fiber is superior in dimensional stability and price competition to the nylon fiber. In this respect, more polyester fiber has been increasingly used in the tire code filed. However, the polyester fiber is not appropriate for the tire of the car driven with high speed due to low heat resistance and deteriorated adhesion to rubber.
The cellulose-based modified natural fiber such as rayon fiber has the great strength retention rate and dimensional stability. However, the cellulose-based modified natural fiber may be deteriorated in its strength by moisture. Thus, it necessarily requires a complicated process for preventing the moisture in a method for manufacturing the tire using the cellulose-based modified natural fiber.
In the meantime, it is required that strength and modulus in tire-reinforcing fiber cord used for heavy equipment vehicle, racing car, airplane, and agricultural vehicle be higher than those in the polyester or nylon fiber.
The fiber which can provide the high strength and modulus is aramid fiber, that is, one kind of aromatic polyamide fibers.
However, the aramid fiber has high modulus and low elongation. Thus, if fatigue is repetitively applied to tire cord prepared with the aramid fiber under the environments of high load and stress, the tire prepared with the aramid fiber may have the following problems due to low fatigue resistance of the aramid fiber.
When the vehicle is driven at high speed, a temperature in the tire of the vehicle is elevated. Especially, since the tire is maintained at high temperature and high pressure during the high-speed driving of the vehicle, the tire-reinforcing fiber cord is exposed to the environments of high temperature and high pressure. In this case, if the fiber cord has the low fatigue resistance, the cord property, especially, the travelling performance is lowered by the deteriorated cord strength. More seriously, the tire may burst during the traveling.